Ink jet printing has become a prominent contender in the digital output arena because of its non-impact, low-noise characteristics, its compatibility with plain paper and its avoidance of toner transfers and fixing as well as lack of pressure contact at printing interface. Ink jet printing mechanisms includes continuous ink jet or drop-on-demand ink jet. U.S. Pat. No. 3,946,398, which issued to Kyser et al. in 1970, discloses a drop-on-demand ink jet printer which applies a high voltage to a piezoelectric crystal, causing the crystal to bend, applying pressure on an ink reservoir and jetting drops on demand. Other types of piezoelectric drop-on-demand printers utilize piezoelectric crystals in push mode, shear mode, and squeeze mode. Piezoelectric drop-on-demand printers have achieved image resolutions up to 720 to 1440 dpi for home and office printers.
Great Britain Patent 2,007,162, which issued to Endo et al. in 1979, discloses an electrothermal drop-on-demand ink jet printer which applies a power pulse to an electrothermal heater which is in thermal contact with water based ink in a nozzle. A small quantity of ink rapidly evaporates, forming a bubble which causes an ink drop to be ejected from small apertures along the edge of the heater substrate. This technology is known as Bubblejet.TM. (trademark of Canon K. K. of Japan).
U.S. Pat. No. 4,490,728, which issued to Vaught et al. in 1982, discloses an electrothermal drop ejection system which also operates by bubble formation to eject drops in a direction normal to the plane of the heater substrate. As used herein, the term "thermal ink jet" is used to refer to both this system and system commonly known as Bubblejet.TM..
The advancement of ink jet printing technologies has opened up opportunities for applications in photo minilab and microlab. In these environments, the ink jet printing techniques have the advantages of easy image manipulation, compatibility with digital image files, and faster turn-around time. When configured properly, ink jet printers can deliver images with qualities comparable to that of the traditional photographs. For digital photo applications, it is crucial to minimize all image artifacts related ink jet printing so that the customers can perceive the digital prints having the similar image quality as the traditional photographs.
Many image artifacts in ink jet printing are caused by improper (i.e. not rapid enough) drying of ink dots on the ink receivers. The ink dots are formed by ink droplets ejected from the ink jet print heads. The drying of ink dots on the receiver can include several stages. First, within each printing pass (or swath), the ink dots freshly placed on the receiver need to dry fast enough so that the ink dots will not merge with each other. The interaction (e.g. merging) of ink dots on the receiver can cause image artifacts such as coalescence and inter color bleeding. For a print head transport speed of 20 inch/second relative to a 20 inch wide receiver, for example, the time scale of this drying stage is in the range of 10 .mu.s to 1 second. Second, after an ink image is printed, the ink receiver needs to be dry on the surface before it can be stacked with other printed images or handled by a customer. This time scale is typically in the range of 10 seconds to 10 minutes, depending on the printing throughput and the size of the ink image.
The drying mechanisms of ink dots on receiver include absorption by the ink receiver and the evaporation to the ambient environment. The ink drying can be accelerated by improving both mechanisms. Absorbant materials are often coated in the ink receiver to accelerate absorption of ink solution into the receiver. Auxiliary drying devices can also be installed in the ink jet printer to assist evaporation of ink into air. Many techniques have been reported in these areas. Examples of the disclosures can be found in U.S. Pat. Nos. 5,141,599, 5,479,199 and EP 761 449 A2. These techniques, however, have the disadvantages in added cost. Furthermore, photo color images usually have high ink coverage; the above techniques often do not dry ink fast enough to eliminate coalescence and color bleeding artifacts.
Artifacts in color ink images also include misregistration between different color planes of a color ink image. For example, if cyan, magenta, and yellow colors are to be sequentially formed on a receiver, if the yellow image plane is printed not in registration with the cyan and magenta color planes, improper colors will result in the formed color ink image.